Diffusion annealing is a heat treatment process also known as homogenization annealing. A treatment method that is kept warm for a long time at a temperature slightly below the solidus temperature, which is used to eliminate the chemical composition and microstructure inhomogeneity in ingots, castings or forgings. The diffusion annealing temperature of steel is higher than Ac3, between 1100 and 1200°C. This process heats the material to a temperature slightly below the solidus, keeps it warm for a long time, and then slowly cools it. The insulation time is appropriately extended, which can achieve the effect of diffusion annealing to eliminate stress.
They always produce dendrite segregation of alloy elements during the solidification process after pouring, that is, chemical composition inhomogeneity. Diffusion annealing is to heat austenitization at high temperature for a long time, so that the unevenly distributed elements can diffuse to eliminate or weaken dendrite segregation.
The commonly used diffusion annealing temperature is 1100℃-1200℃, and the holding time is 10-15 hours. The higher the alloying element content in the steel, the higher the heating temperature used. After high temperature and long-term diffusion annealing, the austenite grains have grown excessively. If no hot working is performed, a complete annealing or normalizing must be performed to refine the grains.
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